In a system in which a relay device for relaying the transfer of e-mail (SMTP communication) and the acquisition of e-mail (Internet Message Access Protocol (IMAP) communication) is installed in a carrier facility network, a following technique was proposed. The relay device compresses e-mail, including a header, transferred from an e-mail transfer server, encapsulates the compressed e-mail with attaching a new header, and transfers the encapsulated e-mail to an IMAP server as compressed e-mail. When an e-mail acquisition request is received from a communication terminal, the relay device decapsulates the compressed e-mail acquired from the IMAP server, decompresses the compressed e-mail, and sends the decompressed e-mail to the communication terminal. Here the relay device changes the parameters, such as the e-mail size, so that compression and decompression of the e-mail do not bring inconsistency among various IMAP commands (see Japanese Patent Application Publication No. 2010-278484).
Another related art of the disclosure that was proposed is an information processing apparatus, having: a data acquiring unit that acquires data, which flows through a network and includes a header and content, before the data reaches a destination; an inspecting unit that inspects the content; an inspection-time transmitting unit that transmits at least a part of the data to the destination while the inspecting unit is performing inspection; and a transfer unit that transfers the data, excluding the portion already transmitted by the inspection-time transmitting unit to the destination after the inspecting unit completed the inspection of the content of the data (see Japanese Patent Application Publication No. 2016-163162).